The central nervous sytem (C.N.S.) is involved in the regulation of hormone secretion from the anterior pituitary by means of hormonally- active substances produced by the brain. Releasing and inhibiting factors, secreted by the hypothalamus, control the rates of synthesis and release of pituitary gonadotropic hormones and prolactin. Of major importance in understanding the relationship between the C.N.S. and pituitary hormones is a clarification of what neurotransmitters are involved in the release of these hypothalamic substances. Recent studies strongly suggest that several amino acids may act as neurotransmitters in the mammalian nervous system, although their effects on anterior pituitary hormone secretion are unknown. The present studies are desiged to ascertain the effects of several neutral amino acids including GABA, glycine, taurine, and alanine, and several acidic amino acids, notably glutamate and aspartate on pituitary release of LH, FSH, and prolactin. Amino acids are injected into the ventricle. Plasma hormone levels are assessed by radioimmunoassay.